1. Field of the Invention
This invention relates to a process for manufacturing spherical objects, especially an occluder for a ball valve as a component of an artificial heart.
2. Description of the Prior Art
In recent years, an increasing effort has been expended in the development of an extra- or paracorporeally-located artificial heart to temporarily assist cardiac function of the natural heart of a patient during open-heart surgery or the like. For example, referring to FIG. 1 in which reference number 10 designates a heart, shown are a pair of sac type blood pumps 11 connected, one between the right atrium and the pulmonary artery and the other between the left atrium and the aorta. Such sac type blood pumps have been studied and used as mechenical assistants to the heart.
Blood pumps 11 of the sac type are composed essentially of a blood (pumping) chamber 2 and a pressure housing or outer casing 1 which is, for example, made of polycarbonate or polyurethane resin and which envelops blood chamber 2 in an airtight manner. Blood chamber 2 has on the top a pair of inflow and outflow parts 3, 4 which project upward substantially parallel to each other and through which blood flows to or from the blood chamber. Housing 1 is flanged (the flange is designated as reference numeral 5) to enclose in an airtight manner chamber 2 therein. Blood inflow and outflow ports 3, 4 are each fitted inside with artificial check valves 6, 7 in order to avoid backflow of blood 17, thus assuring that blood 17 is introduced through blood inflow part 3 into chamber 2 and pumped out pulsatively through blood outflow port 4. Such pulsatile pumping of blood results from the repeated alternate expansion and contraction caused by the alternate variation in outside pressure on chamber 2 in accordance with the repeated alternate introduction of compressed air into chamber 2 and suction of compressed air therefrom through a single port 8 at the bottom of housing 1. Inflow port 3 is connected through a connector 13 to a cannula 12 anastomosed to the heart, each being inserted into the connector from opposite end to the other till the flanged center 14 thereof.
Valve components 6, 7 of such blood pumps as above-stated may be, for example, a disk or a ball valve. The latter comprises a movable ball which is highly durable and exhibits little risk of thrombosis compared with the former. Both type of valves, however, have the difficulty of involving disturbance of the blood stream which is due to the provision of the strut and cage of the valve in blood stream. This can lead to thrombus formation.
Japanese Patent Publication No. 42759/1979 is discloses a blood pump comprising ball valves without a strut or cage, as shown in FIG. 2 in which reference numeral 13 designates a connector. It has the following advantages:
(1) It can be manufactured by a simpler process with a smaller number of parts and with simpler and inexpensive molds. PA1 (2) It has a good response characteristic: the ball in a ball valve can be instantly moved from one position where the ball is placed in point contact with a valve seat 21a to allow blood 17 to pass between ball 28 and the valve body 20 to a second position where the ball is placed in total contact with a valve seat 21b preventing backflow of blood 17. PA1 (3) It is made of plastic and rubber and has relatively good durability.
The above-mentioned balls 28 are usually made of rubber such as silicone and their sphericity is most important for the ball valve. Inadequate sphericity affects the formation of a clearance between the ball and the valve seat, which can result in a misalignment wherein the device fails to prevent backflow. As a counter-measure against this, a ball obtained by casting, injection molding, or the like, is surface-polished. In general, however, precise polishing of a formed rubber object is accomplished only with much difficulty.